By Markham Heid
March 25, 2014

You tell a friend you love her skirt when it's actually hideous: small lie. You tell your boss you delivered the proposal on time, when in fact it was late-and so your firm was disqualified: big lie.

Like the people who tell them, lies come in all shapes and sizes. And depending on the size, a falsehood can have profound effects on your brain and body, starting the instant the words pass your lips.

00:01:00: The moment you lie, the stress of formulating a story causes your nervous system to release cortisol into your brain, says Arthur Markman, Ph.D., executive editor of the journal Cognitive Science. If the lie is massive, you may even experience an adrenaline rush, he adds: Your heartbeat quickens, your pupils dilate, and you begin to sweat. Your brain recognizes that your lie may have put you in danger, so the fight-or-flight response kicks in as you gear up to defend yourself.

00:05:00: After a few minutes, your brain has to keep track of what you know and what you told the other person. And that's very taxing-especially for your working memory, which is involved in decision-making and problem solving, Markman explains. As a result of this increased workload, your brain's ability to make smart decisions suffers. This may be why some liars compound a first, small-ish lie with bigger untruths, he says: Their brains are struggling to work out the effects of their deception, so they may overlook simpler, smarter alternatives to lying.

00:10:00: With more time, you could become angry, especially toward the person you lied to. You lash out in order to shift the focus off your dishonesty and onto something else (your questioner's nosiness, maybe)-think about teens slamming doors or screaming when caught. Adults learn to handle this better, but they still go on the offensive. Because your brain recognizes that there are alternatives to your tall tale (the truth, for one), you may also feel compelled to explain your actions, Markman says.

00:30:00: The stress hormones have dissipated and you may feel worried, Markman says. To counter these feelings, you may become very apologetic or sweet to the person you deceived. On the other hand, you may demonize that person (or people) in order to feel superior, he says-that's your brain trying to justify your lie by telling itself the person you lied to somehow didn't deserve the truth.

24:00:00: For habitual fabricators, you've discarded reality 24 hours later, and you're focused on "living the lie." In time, you may even lose track of the truth, Markman says. But for people unaccustomed to lying, your brain clings to residual negative feelings about the dishonesty. You also may feel something called negative affect, Markman explains. Because seeing her reminds you of your deception, you avoid her or act coldly. "We're wired to avoid situations or people that make us feel bad about ourselves," he adds.

72:00:00: The burden of living with your whopper can cause chronic anxiety. The continuing circulation of stress hormones like cortisol in your brain hurts your ability to think clearly and depresses your immune system. As a result, you're more likely to catch a cold. You also may have trouble sleeping, which intensifies these issues. "Sleep removes the emotional tone of your memories," Markman says. "If you're sleeping poorly, you continue to experience negative emotions, even though time has passed." While these harmful responses eventually fade, they could pop up again if you feel your lie may be exposed, he explains. "Telling the truth may get you in trouble, but in the long run, it'll feel better to get things out in the open."